The 3rd Generation Partnership Project (3GPP), a standard-setting organization that develops specifications for wireless communications systems, is studying and developing Long Term Evolution-Advanced (LTE-Advanced), which is an advancement of LTE, a mobile communications system. Although work for specifying basic functions of LTE-A has been completed, with an aim to further improve performance and improve the capacity to handle diversified system operation scenarios, the introduction of new functions has been proposed, discussion continues, and the system continues to advance. Under the LTE-A specifications thus far, a wireless control signal for transmitting radio parameters (the position of the frequency domain, the modulation scheme, the code rate, etc. for a data signal) directly related to the wireless transmission of a data signal that is to be transmitted, has been transmitted at a time domain that differs from that of the data signal. In other words, the radio resource domain used in the transmission of the wireless control signal and the radio resource domain used in the transmission of a data signal have been time-division multiplexed. The latest discussions study a way to also map wireless control signals in the domain used for the transmission of data signals to enable the amount of radio resources that can be used in the transmission of a wireless control signal to be increased as circumstances demand. Nonetheless, if a portion of the domain for the transmission of data signals are made available for the transmission of wireless control signals as well, the amount of radio resources that can be used for data signal transmission decreases. Therefore, the use of a highly efficient transmission method and a minimal amount of radio resources is desirable for wireless control signals that are to be transmitted on the domain used for data signal transmission. One such known method is the application of a modulation scheme of a high-order modulation degree to the wireless signals and in which a high-order modulation scheme is applied to downlink control signals in a vicinity of a reference signal (for example, refer to Published Japanese-Translation of PCT Application, Publication No. 2007/052767). In the reception and demodulation of a wireless signal to which a high-order modulation scheme of using not only 16 QAM, 64 QAM, etc. phase components but also amplitude components and mapping information bits is applied, demodulation characteristics have to be enhanced. Normally, the demodulation characteristics of signals in the vicinity of a reference signal improves when data signal demodulation is performed by interpolating channel estimation results for multiple reference signals to obtain channel estimation information for demodulating data signals.
Nonetheless, for example, as with LTE and LTE-A, if the transmission frequency of a common reference signal among wireless cells is shifted, even if a wireless control signal to which a modulation scheme of a high-order modulation degree is applied is in the vicinity of the reference signal, reception characteristics of the control signal may deteriorate consequent to interference from the common reference signal of an adjacent cell, and the benefit of improved demodulation characteristics by placing in the vicinity of a reference signal, a signal that is to be demodulated cannot be sufficiently obtained.